This invention relates to an electric blender, normally for use in the kitchen. Such blenders are well known and comprise a base unit including a drive motor for rotating a number of blades in a container for holding the material to be blended.
There is a potential danger if the blades can be rotated when the top of the container is fully open because a hand or the like may be inserted into the container in an attempt to insert produce to be blended into it or to push such produce towards the blades.
It is known for example from GB-A-2134804 for a blender to include a switch means which disables the motor if the jug container is not present on the base unit. However, the means for enabling the motor comprises a projection on the base of the handle of the container jug and this does not ensure that the jug is effectively closed against insertion of a hand.
It is also known from U.S. Pat. No. 5,779,358 to disable the motor in a blender if the weight on the base unit is not sufficient. However, again this does not ensure that an effectively closed container is present.
It is also known, for example, from U.S. Pat. Nos. 4,111,372, 4,373,677, 5,323,973, 4,200,240 and EP-A-0257705, for the base unit to include an upwardly extending projection or stalk extending substantially to the height of the container when located on the base unit, in which switch means is located, which switch means is biased to a position in which it disables the drive motor but which is operable by the correct positioning of a lid on the container to enable the motor. The lid is assumed to be at a given height, accurately defined in relation to the switch means, and in most of the above examples is rotated when at this height to the correct enabling position. While the switch operating probe on the lid may, for example as in the case of U.S. Pat. No. 4,111,372 move downwardly as the lid is correctly positioned, so as to move a switch button downwardly to operate the switch, there is no provision for a broad tolerance range in the correct lid height. This would in practice be unnecessary in the case of the blender of U.S. Pat. No. 4,111,372, because the container is made of plastics material which can be manufactured t close tolerances and the container height is less than its diameter.
We have found that using a glass container, which preferably has a height greater than its largest diameter, the manufacturing tolerances tend to provide products having heights which may be 2 mm smaller or larger than that specified and errors in concentricity up to 4 mm either side of that specified. If such a glass container is provided with a lid arranged to interact with an enabling/disabling switch in an upward projection from the base, a rotational movement of the lid is unreliable in operating the switch. A downward movement of an operating member on the lid may also be unsatisfactory since if the container is higher than that specified the operating member may not reach the switch contact, while if the container is shorter than specified, engagement of the operating member with the switch contact may prevent proper closure of the lid. The operating member may also be displaced sideways from the position of the switch due to the lack of concentricity.
The present invention relates to an electric blender with a safety interlock that prevents the motor of the blender from being operated unless the container is on the base unit with the lid properly positioned thereto. The electric blender of the present invention includes a base unit incorporating an electric motor and a separable container in the form of a glass jug having a handle and a removal lid. The base unit includes a hollow upstanding projection at one side. This projection extends to a height just above the level of or substantially level with the top of the container without the lid. The interlock switch includes a leaf spring connection arm that is located in the hollow upstanding projection that connects to a control circuit between the motor and a power source. The interlock switch is normally in an open condition so that the motor is disabled as the motor does not receive power. A closed topped actuator is mounted in an upper portion of the hollow upstanding projection for vertical movement and is biased upwardly away from the leaf spring arm by an internal spring. The actuator is movable downwardly to flex the spring arm substantially horizontally to effectively close the interlock switch to enable a condition allowing the motor to be connected to the power source upon closure of an on/off switch. The lid includes an arm having a downwardly extending switch operating projection such that when the container is located on the base unit, and the lid is correctly engaged with top of the container, the projection engages a plunger and presses it into a position in which the interlock switch is moved to the enabled condition.
An object of the present invention is to provide a blender which includes safety switch means which prevent the motor being operated unless the container is on the base unit and its lid is correctly positioned. A further object is to provide such a blender in which a safety switch will be operated despite tolerance differences in the height and preferably also the concentricity of the container.
Accordingly, in a preferred form, the invention provides an electric blender comprising a base unit having an electric motor and an upwardly extending projection, connecting means for connecting the motor to a power supply, a separate glass container incorporating rotatable blades and engageable with the base unit so that the motor, when connected to the power supply will drive the blades, a lid for closing an open end of the container but separable therefrom, interlock switch means located in the projection and operable between conditions in which the motor is enabled or disabled with the interlock switch means biased to the motor disabled condition, a downwardly extending operating member integral with the lid and arranged to operate the interlock switch means to the motor-enabled condition in a safe condition when the separate glass container and the lid are correctly engaged with one another and the separate glass container is engaged with the base unit, an actuator movable substantially vertically within the projection and extending between the operating member and the interlock switch means in the safe condition, wherein the interlock switch means has a switch arm which comprises a flexible leaf spring movable substantially horizontally by direct interaction with the actuator on downward movement of the actuator, and wherein the substantially horizontal movement of the flexible leaf spring closes the interlock switch means to place the motor in a motor enabling condition and in which the actuator is arranged to operate the interlock switch means to the motor-enabled condition despite variations in the height and preferable also the concentricity of the separate glass container.
Preferably the actuator is arranged to first contact the switch to move it to enabled condition when the lid is correctly positioned on a container which has a height above the specified height, for example 2 mm above that height, and the actuator can move downwardly, preferably 4 mm, past that position in which it first contacts the switch.
The head of the actuator has sufficient dimensions horizontally that it will be contacted by the operating member in the safe condition despite horizontal variations in the position of the lid by up to 8 mm.
The plunger has sufficient dimensions horizontally that it will be contacted by the operating member in the safe condition despite horizontal variations in the position of the lid by up to 8 mm.
One embodiment of electric blender, in accordance with the invention, will now be described, by way of example only, with reference to the accompanying drawings of which: